The present invention relates to aluminium alloys for use as bearing materials, for example for use in internal combustion engines.
For these applications, one known bearing material is Al Sn20% Cu1%. This is a widely used bearing material having good fatigue strength and seizure resistance, and being able to perform happily against forged steel and cast iron journals without the use of an electroplated overlay. Changes in engine design have resulted in the increased use of turbocharged petrol engines and high speed diesel engines for automotive applications. This has provided a requirement for a bearing alloy capable of being used against forged steel and cast iron crankshafts without an electroplated overlay with a higher fatigue rating than Al Sn20 Cu1.
Good anti-seizure properties and high fatique strength are conflicting requirements in an engine bearing alloy, since the latter is associated with high hardness and the former is associated with low hardness.
One known high strength bearing alloy is Al Si11% Cu1% in which the silicon is finely and uniformly distributed. The anti-seizure properties of this alloy derive from the uniform dispersion of fine silicon particles and the presence of the copper; both these elements help to provide a degree of fatigue strength. The high fatigue strength is still further increased by the provision of an electroplated overlay of lead/tin over a nickel or copper/zinc interlayer.
This Al Si11 Cu1 alloy has become well established commercially as the lining of steel backed crankshaft bearings in internal combustion engines, particularly high speed diesel engines.
However, the high silicon content renders the alloy unsuitable for bore broaching techniques which can be very much more economical as a mass production technique than the use of conventional boring machinery.